Solid polymeric matrices containing rhodamines and their use in lasers

ABSTRACT

The present patent of invention describes the obtention of lasers in solid condition of dyes of the family of Rhodamines. More particularly, it describes lasers in which said dye or chromophore is to be found covalently anchored to a solid matrix, consisting in a transparent organic polymer and suficiently stable to the pumping radiation. Its application is the production of the laser emittance by an organic dye in a solid matrix and polymers containing rhodamines.

This appln. is a 371 of PCT/FS96/00139, filed Jun. 28, 1996.

Dye lasers are profusely applied in very different fields. For example,they are used every day more and more in Medicine for the selectivedestruction of tissue, by means of the so called photodynamic therapy,and for the “in situ” diagnosis of possible tumours. However, both inthe industrial field and in their medical applications, the employmentof dye lasers implies the use of dyes in solutions, which signifies aseries of disadvantages and limitations, which are: the employment oforganic solvents, some of which are toxic and volatile, the maintenanceof a constant flow of the dye solution within the cavity of the laser;and other tedious operations, such as having to renew the dye solution,or else replace it when a change of spectral region of the emittance ofthe laser is desired. For this, the availability of solid dye lasers,with notable advantages over liquid lasers is of great technicalinterest, since besides being more compact with a notable decrease inits size, it allows working in the absence of solvents, a particularlyimportant aspect during its clinical use, and also, with a minimummaintenance, capable of changing the spectal interval of the laseremittance in a rapid and simple manner. Other additional advantagesderived from the use of a solid dye laser are, the freedom of design ofthe cavity and the low cost of the same when the solid is a polymer.

A laser is a luminous source, the light of which, monochromatic andcoherente, originates from the emittance stimulated by the radiation ofa material. As its name indicates, the stimulated emittance is the onewhich is caused by the disactivation of previously excited conditionscaused by the actual radiation emitted by the material. If said materialis a fluorescent colorant, the laser is called of dye. Attending to theenergetic levels implied by the laser emittance, the dye lasers may beconsidered as four level lasers.

The basic operational mechanism of a dye laser is herewith described. Ifa dye solution for laser is illuminated with light with a wave lengthwhich falls within its absorption band (pumping radiation), themolecules of said dye are excited from the fundamental level singletS_(o) up to some rotovibrational level of the first excited singletcondition S_(i). Due to collisions with other molecules, the excess ofrotovibrational energy is rapidly dissipated in the form of heat, andso, the molecule relaxes to a rotovibrational level below S₁. In S1condition, the molecule may emit spontaneous fluorescent radiation,passing to any rotovibrational level of fundamental conditionl S_(o).Finally, relaxation non radioactive processes carry the molecule torotovibrational level zero from fundamental condition. The light emittedhas always a wave length which is longer than that of the pumpingradiation, due to the fact that part of the excitment energy isdissipated by non radioactive processes. If the dye is excited at thesecond excitment singlet, or level S₂, or at other higher levels, themolecule may decline by non radioactive processes to condition S₁. Ifthe intensity of the pumping radiation is sufficiently high, for example100 kw/cm², it may be achieved that the number of molecules in excitedcondition S₁ be superior at all times to that of the molecule infundamental condition S_(o) (population reversal), the stimulatedemittance or laser being then possible throughout all the fluorescentband, with the exception of the part which overlaps with the absorptionband.

STATE OF THE ART

The dyes available for use as a source of laser radiation, obtained byorganic synthesis, over a wide spectral zone, from 340 nm (stilbenes) upto 1200 nm (cyanines), all present high monochromaticity in theemittance and the majority operate as has just been described. In thepractical application of this type of dyes two limiting factors exist:a) the photostability, since the dyes must support very high pumpingenergies and a prolonged exposure to radiation, which may cause itsdegrading, losing effectivity as emitting sources; and b) syntonizationinterval since the majority of the normal dyes have only small wavelength intervals in which the the laser efficiency is acceptable.

The use of a laser dye solution in a solid medium has evident technicaladvantages as regards the use of a liquid medium; the sample is moremanageable and attainable, generally of low density, easily machinable,etc. The stimulated emittance generated by Rhodamine G dispersed inpoly(methyl methacrylate) was described for the first time in 1967 bySöffer and McFarland [Appl. Phys. Lett. 10, 266(1967)] and thestimulated emittance of rhodamines B and 6G dispersed in the samepolymer was described a year later by Peterson and Snavely [Appl Phys.Lett 12 238(1968)]. Since then, a great variety of solid matrices havebeen described (polycarbonates, polystyrene, polyvinylalcoholes andpolyacrylates) in which diverse types of dyes have been dispersed.

However, due to the generally scarce resistance of the polymeric matrixto strong pumping radiations, as well as to the generally low thermalstability of the dyes, its extensive use has been impossible up to thepresent. None the less, the work carried out by O'Conell and col.[Opt.Eng. 22 393(1983)] indicates that the duly purified poly(methylmethacrylate) is a polymer which is resistant to intense radiation.Another additional difficulty lies in the low solubility of the laserdyes, developed up to this moment in the majority of conventionalpolymers. In fact, in the described examples in the literature, the dyeis not to be found really disolved but in the majority of the cases,dispersed in the matrix.

A detailed description of the state of the art has been recentlypublished by our working group [R. Sastre, A.Costela, Adv. Mater. 7, 198(1995)]. In reality, our working group has managed to obtain laseremittance, with reasonable efficacy and an incremented photostability asregards previous works, with real solutions of Rhodamine 6G dye andRhodamine 640 dye in polymeric matrices (poly (methyl methacrylate),poly (methacrylate 2-hydroxyethyl)) [F.Amat Guerri, A.Costela, J.M.Figuera, F.Florido, I.García-Moreno and R.Sastre, Opt. Commun. 114,442 (1995), R.Sastre and A.Costela, Adv. Mater. 7 198(1995); A.Costela,F.Florido, I. García-Moreno, R Duchowicz, F.Amat Guerri, J. M.Figueraand R. Sastre, Appl. Phys. B, 60, 383 (1995)].

The only works (including a registered patent) on solid materials fordye lasers in which the dye is to be found in covalent anchorage with apolymeric matrix, has been published by our group. With other purposes,especially the photostablization of solid polymers, polyers have beendescribed in which a chromophore with an ethylenic substitute has beenintroduced in the polymeric chain by copolymerization. Used as monomersin said works with a different purpose were among others, acrylates,styrene and vinyl chloride [F. A.Bottino, G.Di Pascuale and A.Pollicino,Macromolec 23,2662(1990); K. P.Ghiggino, A. D.Saully, S. W.Biggen and M.D.Yandell, J.Polym, Sci. Part C; Polym. Lett 26, 505(1988); D.B.O'Connor, G. W.Scott, D. R.Coulter, A.Gupta, S. P.Webb, S. W.Yeh andJ. H.Clark, Chem.Phys. Lett 121,417(1985)].

DESCRIPTION OF THE INVENTION

The present invention is based on the use of a series of dyes with acommon structure; the xanthene skeleton substituted by phenyl inposition 9, and which in position 2′ of said phenyl, possesses a groupof esterified carboxyl by an R group with an unsaturation which may bepolymerized.

The introduction of the unsaturated R group in the dye molecule ispreferably carried out by a reaction between a Rhodamine having a freecarboxyl group in position 2′(R═H), and an unsaturated halogenatedderivative, performing the reaction in the presence of a base, such asanhydrid solid carbonate. The reaction between carboxylic acid salts andhalogenated derivatives, especially allylics or benzylics is well knownas a manner of obtaining, generally with good efficiency, esters of saidacids.

For example, the reaction between Rhodamine 19 and a free carboxyl groupin position 2′, and allyl chloride leads in the corresponding allylicester, a compound which maintains the chromophore intact and which mayadditionally copolymerize by the double allylic union with conventionalmonomers.

In the present invention is also patented, the introduction in the dyemolecule of unsaturated groups in the same position 2′, through spacergroups which possess an allylic or benzylic halogen. Thus, thechromophore is more distanced from the polymer chain than in theprevious case, which presents advantages in some cases, also being ableto use greatly varied polymerizable groups without being limited to themonomers which possess a halogen in their molecule.

As an example of a halogenated derivative which possesses a spacer groupbetween the halogen and the monomer, we propose a benzyl chloridesubstituted in position para by group CO₂(CH₂)_(n)OCOC(x)═CH₂ where nmay be comprised between 1 and 18, and X may be H, methyl, ethyl, etc.Said benzyl chlorides are obtained by the reaction between thepchloromethylbenzoic acid (ClCH₂—C₆H₄—COCl) and the correspondingunsaturated alcohol HO—(CH₂)_(n)OCOC(X)═CH₂.

Incorporation of the Dye to a Polymeric Matrix

The present invention incorporates the dye to a polymeric solid matrix.Said incorporation may be performed in three well differentiated ways:

a) by covalent union to a functionalized polymer, either as a lateralsubstituent of the main chain of the polymer or as a terminal group ofthe same.

b) by direct copolymerization of the monomeric dye.

c) by incorporation, as additive, of the previous copolymer to anotherpolymer or copolymer.

The three procedures mentionned for Rhodamines, capable of emittinglaser light by means of the classical mechanism, are described asfollows:

a) Covalent Union of the Dye to a Functionalized Polymer

In this case, the polymer shall posses in its molecule, a group orgroups capable of reacting with a Rhodamine possessing in position 2′, afree carboxylic group. In order to help the reaction, the reactive groupof the polymeric chain may be an allyl halide or even better, of benzyl.

The reaction of the modification or anchorage of the chromophore to thepolymer is carried out using generally common techniques and proceduresused in organic synthesis for the corresponding reactions between bothfunctional groups in molecules of low molecular weight, with the onlylimitation being, that said synthesis procedure shall not alter thestructure nor the composition of said previously described generalformular chromophore, nor introduce any other modification which altersthe properties of the laser light emittance of said molecules.

For the use of the resultant polymer, once covalently joined to theactual dye, in the application which is the object of the present Patentof invention, it is advisable to carry out a previous, carefulpurification of the same. For this, the most suitable methods are therepeated solution and precipitation, or direct ultrafiltration.

b) Direct Copolymerization of the Dye

In this case, the Rhodamine dye, with R rest containing an unsaturationof the type previously described, is copolymerized with one or variousmonomers in which the monomeric dye is soluble. The unsaturatedsubstitute R may be any of the following groups:

—(CH₂)_(n)CH═CH₂

—(CH₂)_(n)C(CH₃)═CH₂

 —(CH₂)_(n)OCOH═CH₂

—(CH₂)_(n)OCOC(CH₃)═CH₂

—(CH₂)_(n)(p)C₆H₄—CO₂(CH₂)_(n)OCOCH═CH₂

—(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂

The previous groups may be joined to the carboxyl group in 2′ throughspacers of type —(OCH₂)_(n) ⁻(OCH₂CH₂)_(n) ⁻; —O—(CH₂)_(n) ⁻. In allcases, the n value may be between 0 and 12.

For the purposes which are the object of the present Patent ofInvention, the previously indicated compounds may be directlypolymerized by addition, though it is preferable to copolymerize thesame with ethylenically unsaturated monomers, preferably mono andpolyfunctional monomers of the vinylic type, acrylic or methacrylic typeand their mixtures and combinations. The election of the monomer ormonomers is conditioned, in the first place, by its compatibility withthe compounds with the described formula, understanding bycompatibility, the solubility of the same, without alteration of thestructure of the chromophore group. In second place, said election isalso conditioned by the necessity that the polymers coming from saidmonomers do not present light absorption in the region comprised between337 and 700 nm.

The copolymerization between the previously described dyes and theselected monomers may be carried out in solution, suspension, emulsion,interphase, block or mass. The polymerization process may be thermallyor photochemically initiated, preferably by using a generator of freeradicals, such as benzoyl peroxide o α,α′-azoisobutyronitryl.

It is advisable to carry out the polymerization with vacuum (at least at15 Pa) or else at normal pressure, though below an inert atmosphere suchas that of nitrogen or argon.

The initial relation between the concentration of the dye and that ofthe monomer, or mixture of monomers, shall not exceed in any case, value1.1 in volume, adjusting the proportion of each compound depending onthe final absorption desired at the excitation or pumping laser wavelength, depending in turn, for each case, on the molar absorptioncoefficient of the specific dye, considering the contraction of thevolumen experimented by the resultant inital solution when polymerized.

The use of polyfunctional nomomers leads to the obtention of interlacedpolymers in greater or lesses extension. The degree of interlacingreached in the final polymer depends on the degree of functionality, ornumber of double olephynic interlaces in the stock monomer molecule, andon the proportion or concentration of the same in the initialdye-monomer solution. It is advisable, for the objects to be attained inthe present Patent of Invention, that when one or more polyfunctionalmonomers are employed, the polymerization be performed as a block, inmolds, with one geometric configuration similar to the one it is desiredto have when the polymeric material is going to be employed in thegeneration of the laser light. In any way, the obtained interlacedpolymer may be machined to the geometric shape desired, usingconventional tecniques and tools.

The structural characteristics of the polyfunctional monomers employedin the present case are the same as those previosuly described formonofunctional monomers.

c) By Incorporation of the Polymeric Dye as Additive to Another Polymer

In this case, a polymer or copolymer containing a Rhodamine chromophorecovalently anchored, is added to another polymer or copolymer. Thepolymeric dyes may be incorporated as additives to other polymers in thedesired proportion, suitable to the objects to be attained in thepresent patent of invention, by means of the conventional techniquesemployed with this purpose in the industry of polymers, considering thatthe additive procedure employed shall not alter the structure nor thechemical composition of the additive. The polymers to which thepolymeric dyes may be incorporated are all those polymers and copolymerswhich are commercially in existance, with the only limitation that thesame do not significantly absorb light in the region comprised between337 and 700 nm. So that the emittance of light stimulated be efficient,it is advisable that the polymeric dyes be suitably found disolved inthe polymer. In accordance with the technique of the present invention,the polymer or copolymer to which the previously indicated polymericdyes are incorporated, may be lineal, branched or interlaced andpreferably, of acrylic, or methacrylic type, or a mixture of both ortheir copolymers.

Among the acrylic and methacrylic polymers which are most suitable fortheir use in the present patent of invention, the alkyl polyacrylates orthe alkyl polymethacrylates are the most advisable, in which the alkylgroup has from 1 to 12 carbon atoms, for example, methyl, ethyl, propyl,butyl, pentyl, hexyl, octyl, nonyl, decyl, undecyl and dodecyl, andtheir isomers. Being also includable, the poly acrylates orpolymethacrylates, substituted, lineal branched or interlaced, providedthat their substituents do not interact with the additive.

Another form of incorporating as additive, the said polymeric dyes is bymeans of a preliminary solution in a monomer or mixture of monomers,ethylenically unsaturated and susceptible of being polymerized byaddition. All ethylenically unsaturated, monofunctional (anethylenically unsaturated group by molecule) or polyfunctional (at leasttwo ethylenically unsaturated groups by molecule) monomers, capable ofdisolving the previously indicated polymer dyes, forming with the same,real, homogeneous solutions, with suitable concentration for the objectsto be achieved in the present patent of invention are suitable. The mostsuitable monomers are the vinylics, acrylics and methacrylics, the alkylacrylates or methacrylates being specially advisable, in which the alkylgroup possesses from 1 to 12 carbon atoms. Also includable are thevinylic, acrylic and methacrylic substituted monomers, provided theirsustituents do not interact with the polymeric dye.

The solution of the polymeric dye in the monomer or mixture of monomers,monofunctional or polyfunctional, may polymerize using any commoninitiator used for this purpose, the use of generator initiators of freeradicals via thermal means being preferable in the present application,(as for example, peroxides, hydroperoxides, azocompounds, etc.), viaphotochemical means (as for example, benzoine derivatives, aromaticketones, α-hydroxyketones, acyloximes, thioxanthones, etc), or by meansof a redox process (as for example, using mixtures of iron salts withhydrogen peroxide, etc.).

Laser Device

The polymeric matrices which are the object of the present invention,are used as active means for the generation of laser radiation on thevisible spectral zone.

The polymeric matrices which comprise the laser medium (medium by whichlaser radiation is to be emitted) may be produced in different geometricshapes, though the most advantageous are 2 cm height solid cylinderswith variable diameters, and with a minimum value of 1 cm. Two differentassemblies may be used: a) cutting throughout the length of the cylinderaxis, with the object of obtaining a flat lateral surface, and b) usingthe sample without said cut. In the former case, all flat surfaces ofthe cylinder may be polished until a laser quality is achieved. In thelatter case, the polishing shall cover all the surface of the cylinder.

The sample is placed in a standard laser cavity. Three types of cavitiesmay be used:

(i) Flat-flat cavity, formed by a totally reflectant mirror at theemittance wave length of the laser medium and with a window which actsas outlet coupler.

(ii) Flat-flat cavity, formed by a totally reflectant mirror at thelaser medium emittance wave length and one side of the cylinder whichconstitutes said laser medium, used as outlet coupler.

(iii) cavity as in (i) with added intracavity elements (prisms,difraction network, ethalones) which allow the syntonization of thelaser emittance and the narrowing of the band width.

The material is pumped in cross direction with pulsed radiation comingfrom a laser, for example N₂ with energies in the order of 2-3 mJ. Thepumping radiation is focused on the side surface of the sample (on theflat side surface in the first of the assemblies previously described),by means of a combination of spherical and cylindrical quartz lens, sothat a line of approximately 20×0.25 mm is obtained. In turn, theconcentration of the active medium in the sample is selected so that thepumping radiation is totally absorbed at a depth of approximately 0.25mm.

The material, with the flat side surface, is shifted by means of asuitable device, with pitches of 0.1 to 0.4 mm, at a rate such, thateach region is only once irradiated with the pumping radiation. Forexample, if the rate of repetition of the pumping laser is 1 Hz, thesample shall move in pitches of 0.25 mm per second. Once the edge of theflat zone has been reached, the direction of the displacement isreversed until the other edge has been reached, and thus successively.

In the case of totally cylindrical polymeric matrices, the materials arerotated continuously, also with pitches of 0.1 to 0.4 mm. The rate withwhich the material is rotated, is adjusted in the same way as for thecase of materials with flat side surface. For rotating the cylindricalmatrices, the same are attached by the central part of the lateral sides(according to the axis of the cylinder) so that during the rotation, thepumped region which is to emit the laser radiation, always remains wellaligned within the cavity.

EXAMPLES

At title of example, a description is herewith given of the obtention oftwo Rhodamine molecules which possess a copolymerizable ethylenicsustituent with a monomer which is also etylenic (see figures), as wellas the embodiment of the copolymerization. All products are identifiedunequivocally by the general techniques in the analysis of organiccompounds. Also described as example is the result to be evaluated, inthe described device, of the copolymers as emitters of laser light.

Obtention of Stock Products and of Pattern Dyes

p-chloromethylbenzoate of Ethyl (Cl-Bz-Et)

Obtained by treating the p-(choromethyl)benzoyl chloride with an excessof ethanol. Said latter chloride is obtained, in turn, by treating thep-methylbenzoyl chloride with phosphor pentachloride (according to R.D.Kimbrough and R. N.Gramlett, J.Org.Chem. 1969,34, 3655).

Metacrylate of 2-[p(chloromethyl)benzoyloxy]ethyl (Cl-Bz-MA)

In a flask containing a solution of methacrylate of 2-hydroxyethyl(HEMA) (10 mmol) and tryethylamine (11 mmol) in dry acetone (20 mL),add, drop by drop, under agitation and externally cooling with ice, arecently obtained chloride solution of p-(chloromethyl)benzoyl (11 mmol)in acetone (10 mL). The mixture is left to react at room temperatureduring 1 hr and the solvent is evaporated in vacuum. The liquid residue,after being washed with dry hexane, is used without furtherpurification. Yield 89%.

p-(methoxycarbonyl)benzylic Ester of Rhodamine 19 (Rh-Bz-Et)

A mixture of Rhodamine 19 (250 mg. 0.6 mmol), Cl-Bz-Et(150 mg, 0.75mmol) and N,N-dimethylformamide (15 mL) is heated at 50° C. during 5days, in the absence of light, under agitation and in a nitrogenatmosphere. The evaporation in vacuum of the solvent causes a solidwhich is purified by passing through two successive chromatographycolumns (silica gel, 500 mL of methylene-ethanol chloride 3:2 v/v aseluant for the former, and 200 mL ethyl acetate, followed by 300 mLethyl-ethanol acetate 1.2 v/v t of 200 mL of ethanol, for the latter).The ester Rh-Bz-Et thus isolated (red crystals) is washed with hexaneand vacuum dried. It gives one single stain in thin layer chromatographyin various eluants. Yield 36%.

R X Rhodamine¹⁹ H ClO₄ Rhodamine_(G) CH₂—CH₃ Cl Rh—Al CH₂—CH═CH₂ OHRh—Bz—Et

OH Rh—Bz—MA

OH

Obtention of Rhodamine Monomers Example 1 Obtention of Allylic Ester ofRhodamine 19 (Rh-Al)

A mixture of Rhodamine 19 (200 mg, 0.44 mmol), allyl chloride (0.9 mL,11.1 mmol), anhydrous sodium carbonate (204 mg, 1.9 mmol), hydroquinone(trace) and N,N-dimethylformamide (25 mL) is heated at reflux underagitation, in the absence of light and in a nitrogen atmosphere, during30 hr. The evaporation of the solvents leads to a mixture from which isseparated the Rh-Al allyl ester by chromatography in column (silica gel,chloroform-methanol 85:15 v/v as eluant). The resultant solid gives onesingle stain in thin layer chromatography in various eluants. Theproduct, once dry, is used without subsequent purification. It gives onesingle stain in thin layer chromatography in various eluants. Yield 36%.P.f.238-240° C. Uvvis (EtOH): λ_(max)530 nm, ε80.900 M⁻¹ cm⁻¹.

Example 2 Obtention of p-[2-(Methacryloiloxy)ethoxicarbonyl]benzylicEster of Rhodamine 19 (Rh-BzMA)

A mixture of Rhodamine 19 (414 mg, 1 mmol), Cl-Bz-MA (355 mg, 1.25 mmol)anhydrous sodium carbonate (408 mg, 3.8 mmol) and p-methoxyphenol(traza) in N,N-dimethylformamide (15 mL) is heated at 50° C. during 4days, in the absence of light, under agitation and in a nitrogenatmosphere. The evaporation of the solvent causes a solid which ispurified by passing through two successive chromatography columns(silica gel, 250 mL of methylene-ethanol chloride 3:2 v/v as eluant forthe former, and 150 mL of ethyl acetate, followed by 350 mL of ethylethanol acetate 1.1 v/v and of 150 mL ethanol, for the latter). Theresidue obtained is washed with hexane and vacuum dried. The Rhodamineester 19 Rh-Bz-MA (isolated in the form of ammonium base) is usedwithout ulterior purification. It gives one single stain on thin layerchromatography in various eluants. Yield 44%. Vis (EtPH),λ_(max) 519nm).

Obtention of Copolymers and Terpolymers Example 3

To a homogeneous solution of monomer-dye RhAl (5.7 mg. 0.012 mmol) inmethyl methacrylate (5 ml) and 2-hydroxyethyl methacrylate (5 ml), isadded α,α′-azoisobutyronitryl (10 mg; 0.06 mmol) as initiator. Afterdisolving the initiator, a 12 mm inner diameter cylindrical mold isfilled with the resultant solution. The solution, once in the mold, isdeoxygenized by means of bubbling of nitrogen or pure argon with thehelp of a capilar which is immersed in the solution during a few minutes(5-10 min). The mold is tight locked, under nitrogen atmosphere, andkept at 40° C. during 4-5 days in the dark. Once the sample hassolidified, it is slowly brought to temperature (5° C./day) until the55° C. has been reached, maintaining this temperature during 2 hours.Next, the temperature is again made to rise to 80° C. (5° C./day),slowing cooling to room temperature, finally demolding the cylinder.

Example 4

In identical manner as to that described in the previous example, asolution is prepared of monomer dye Rh-Bz-MA (6.25 mg; 0.01 mmol) in themethyl matacrylate mixture (5 ml) and 2-hydroxyethyl metacrylate (5 ml).Add α,α′-azoisobutyronitryl (15 mg, 0.09 mmol) which is disolved underagitation. The resultant solution is microfiltered with a membrane withpore size 0.2 μm, proceeding to fill the mold described as in theprevious example, following an identical procedure. The mold ismaintained at 40° C. during four days, after which, the temperature isslowly made to rise up to 55° C., keeping this temperature duringanother four days. Next, the temperature is made to rise again (10°C./day), until 80° C. is reached, with the object of eliminating theresidues of initiator which have not decomposed. Finally, slowing coolto room temperature, finally demolding the cylinder.

Example 5 Evaluation of the Polymeric Dyes as Emitters of StimulatedRadiation

The photophysical study carried out in the previously described device,using as laser emitters Rhodamines covalently anchored to methylmethacrylate and 2-hydroxyethyl methacrylate copolymers, is shown inTable 1. Also included are two results of models Rh 6G and Rh-Bz-Et,disolved in HEMA:MMA 1:1 copolymers.

Table 1. Characteristics as emitters of dye lasers of the Rhodaminesfamily disolved in free form in methyl methacrylate and 2-hydroxyethylmethacrylate copolymers or anchored by covalent union to copolymers ofthe same monomers (laser pumping of N₂, at 337 nm; pumping energy: 1.2mJ).

Number of flashes λ_(eemax) Δλ E_(bu) η₁ 15 Compound (nm) (nm) (mJ) (%)Hz 5 Hz 2 Hz Rh6G in P 593 13 0.48 21 8500  8500  8500 (HEMA:MMA 1:1)P[Rh-Al + 589 12 0.48 11 4500  6000  6000 (HEMA:MMA 1:1)] Rh-Bz-Et in P585 10 0.50 16 5000  6000  7500 (HEMA:MMA 1:1) P[Rh-Bz-MA + 594 10 0.4219  900  1700  3500 (HEMA:MMA 3:7) P[Rh-Bz-MA + 587 11 0.58 18 900010500 13500 (HEMA:MMA 1:1)] P[Rh-Bz-MA + 593 10 0.65 18 8000  9000 20000(HEMA:MMA 7:3)] P[Rh-Bz-MA + 591 11 0.56 14 7000  7000 15000 (HEMA:MMA10:0)]

Table 1 shows the maximum wave length of its stimulated emittance(λ_(ee.max)), the band width at medium height of the laser emittance(Δλ), the threshold energy of the pumping (E_(bu)), the efficiency ofthe laser (η₁) and the relative stability of the samples at differentrates s of repetition, expressed as the number of flashes which may besupported on the same position until the 80% of the laser emittance islost.

The properties of compound Rh 6G/P(HEMA:MMA 1:1), in which the Rhodamine6G molecules are simply disolved in the methyl methacrylate and2-hydroxyethyl methacrylate 1:1 copolymer, which have been previouslypublished by us [A. Costela, F. Florido, I. García-Moreno, R.Dochowicz,F.Amat-Guerri, J. M.Figuera, and R.Sastre, Appl.Phys,B 60, 383 (1995)]is included as reference. The high photostability of the materials areto be emphasized, in which the dye is covalently joined to the polymericchain through a spacer (provided that the proportion of MMA in thecopolymer is not high). In fact, when sample [Rh-Bz-MA (HEMA:MMA 7:3)]is assembled on the previously described rotational device, theemittance of the laser continues stable, without significant decrease ofthe emittance after 500,000 shots. As to the efficiency obtained withthe best samples, they are similar to the ones obtained in the sameexperimental system for Rhodamine 6G in ethanolic solution.

What is claimed is:
 1. A solid polymeric matrix containing rhodamine,wherein said matrix comprises polymerized monomers of a rhodaminechromophore having a phenyl at position 9 and an esterified carboxyl atposition 2′ of the phenyl, the matrix, when irradiated, emitting laserradiation, the monomers having the general formula

wherein R¹, R², R³, R⁴, R⁵, R⁶ independently are hydrogen or saturatedalkyl groups of 1 to 6 carbons, and wherein R is an unsaturated groupcapable of polymerization or copolymerization, selected from at leastone of the group consisting of —(CH₂)_(n)OCOCH═CH₂—(CH₂)_(n)(p)C₆H₄—CO₂(CH₂)_(n)OCOCH═CH₂ and—(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂; said R group optionallyjoined to said carboxyl at position 2′ of the phenyl by a spacerselected from the group consisting of —(OCH₂)_(n) ⁻, (OCH₂CH₂)_(n) ⁻;—O—(CH₂)_(n) ⁻, and combinations thereof; wherein n independentlyrepresents a number between 1 and 12; said matrix, when being a polymerof said rhodamine chromophore, hydroxyethyl methacrylate andmethylmethacrylate, comprising a proportion of hydroxyethyl methacrylateto methylmethacrylate of at least 1:1; X is an anion; and wherein saidrhodamine chromophore has been synthesized by reacting rhodamine havinga free carboxylic acid group in position 2′ and an unsaturated halogenderivative selected from the group consisting of substituted andunsubstituted allyl halides, and substituted or unsubstituted benzyl. 2.The solid polymeric matrix of claim 1 wherein said rhodamine chromophorehas been synthesized by reacting rhodamine having a free carboxylic acidgroup in position 2′ and an unsaturated halogen derivative selected fromthe group consisting of substituted and unsubstituted allyl halides, andsubstituted or unsubstituted benzyl, comprising an unsaturated group, atleast one of the allyl group and the unsaturated group being capable ofpolymerizing or copolymerizing with at least another monomer.
 3. Thesolid polymeric matrix of claim 1 wherein the matrix has been preparedby a reaction of polymerization or copolymerization with at leastanother monomer, whereby a solid with the shape of the mold in which thereaction takes place is formed.
 4. The solid polymeric matrix of claim 2wherein said shape is a cylinder.
 5. The solid polymeric matrixaccording to claim 2, wherein the solid is in the shape a cylinderportion having an axial flat lateral surface obtained by cutting acylinder obtained in a cylindrical mold by the axis thereof.
 6. Thesolid polymeric matrix according to claim 2, comprising an active mediumfor generating laser radiation in a spectral zone selected fromultraviolet, visible or infrared adjacent spectral zones.
 7. A solidpolymeric matrix according to claim 1, wherein said anion is at leastone of OH⁻, Cl⁻, or ClO₄ ⁻.
 8. A solid polymeric matrix containingrhodamine, wherein said matrix comprises polymerized monomers of arhodamine chromophore having a phenyl at position 9 and an esterifiedcarboxyl at position 2′ of the phenyl, the matrix, when irradiated,emitting laser radiation, the monomers having the general formula

wherein R¹, R², R³, R⁴, R⁵, R⁶ independently are hydrogen or saturatedalkyl groups of 1 to 6 carbons, and wherein R is a—(CH₂)_(n)(p)C₆H₄—CO₂(CH₂)_(n)OCOCH═CH₂ group capable of polymerizationor copolymerization; said R group optionally joined to said carboxyl atposition 2′ of the phenyl by a spacer selected from the group consistingof —(OCH₂)_(n) ⁻, (OCH₂CH₂)_(n) ⁻; —O—(CH₂)_(n) ⁻, and combinationsthereof; wherein n independently represents a number between 1 and 12;said matrix, when being a polymer of said rhodamine chromophore,hydroxyethyl methacrylate and methylmethacrylate, comprising aproportion of hydroxyethyl methacrylate to methylmethacrylate of atleast 1: 1; and X is an anion.
 9. The solid polymeric matrix of claim 8,wherein said rhodamine chromophore has been synthesized by reacting arhodamine having a free carboxylic acid group in position 2′ and anunsaturated halogen derivative selected from the group consisting ofsubstituted and unsubstituted allyl halides, and substituted orunsubstituted benzyl, comprising an unsaturated group, the allyl groupor the unsaturated group being capable of polymerizing or copolymerizingwith at least another monomer.
 10. The solid polymeric matrix of claim 8wherein the matrix has been prepared by a reaction of polymerization orcopolymerization with at least another monomer, whereby a solid with theshape of the mold in which the reaction takes place is formed.
 11. Thesolid polymeric matrix of claim 10 wherein said shape is a cylinder. 12.The solid polymeric matrix according to claim 10, wherein the solid isin the shape a cylinder portion having an axial flat lateral surfaceobtained by cutting a cylinder obtained in a cylindrical mold by theaxis thereof.
 13. The solid polymeric matrix according to claim 8,comprising an active medium for generating laser radiation in a spectralzone selected from ultraviolet, visible or infrared adjacent spectralzones.
 14. The solid polymeric matrix according to claim 8, wherein theanion is at least one of OH⁻, Cl⁻, or ClO₄ ⁻.
 15. A solid polymericmatrix containing rhodamine, wherein said matrix comprises polymerizedmonomers of a rhodamine chromophore having a phenyl at position 9 and anesterified carboxyl at position 2′ of the phenyl, the matrix, whenirradiated, emitting laser radiation, the monomers having the generalformula

wherein R¹, R², R³, R⁴, R⁵, R⁶ are independently hydrogen or saturatedalkyl groups of 1 to 6 carbons, and wherein R is a—(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂ group capable ofpolymerization or copolymerization; said R group optionally joined tosaid carboxyl at position 2′ of the phenyl by a spacer selected from thegroup consisting of —(OCH₂)_(n) ⁻, (OCH₂CH₂)_(n) ⁻; —O—(CH₂)⁻, andcombinations thereof; wherein n independently represents a numberbetween 1 and 12; said matrix, when being a polymer of said rhodaminechromophore, hydroxyethyl methacrylate and methylmethacrylate,comprising a proportion of hydroxyethyl methacrylate tomethylmethacrylate of at least 1: 1; and X is an anion.
 16. The solidpolymeric matrix according to claim 15, wherein the rhodaminechromophore have been synthesized by reacting a rhodamine having a freecarboxylic acid group in position 2′ and an unsaturated halogenderivative selected from the group consisting of substituted andunsubstituted allyl halides, and substituted or unsubstituted benzyl,comprising an unsaturated group, the allyl group or the unsaturatedgroup being capable of polymerizing or copolymerizing with at leastanother monomer.
 17. The solid polymeric matrix according to claim 15,wherein the matrix has been prepared by polymerization orcopolymerization of the monomers of rhodamine chromophores with at leastanother monomer, whereby a solid with the shape of the mold in which thereaction takes place is formed.
 18. The solid polymeric matrix accordingto claim 17, wherein the solid is in the shape of a cylinder.
 19. Thesolid polymeric matrix according to claim 18, wherein the solid is inthe shape a cylinder portion having an axial flat lateral surfaceobtained by cutting a cylinder obtained in a cylindrical mold by theaxis thereof.
 20. The solid polymeric matrix according to claim 15,comprising an active medium for generating laser radiation in a spectralzone selected from ultraviolet, visible or infrared adjacent spectralzones.
 21. The solid polymeric matrix according to claim 15, wherein theanion is at least one of OH⁻, Cl⁻, or ClO₄ ⁻.
 22. The solid polymericmatrix according to claim 15 wherein R is—(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂ and n=2.
 23. A method ofgenerating laser radiation using a solid polymeric matrix as an activemedium, the matrix comprising polymerized monomers of a rhodaminechromophore, said monomers having the general formula,

wherein R¹, R², R³, R⁴, R⁵, R⁶ independently are hydrogen or saturatedalkyl groups of 1 to 6 carbons, and wherein R is an unsaturated groupcapable of polymerization or copolymerization, selected from at leastone of the group consisting of —(CH₂)_(n)(p)C₆H₄—CO₂(CH₂)_(n)OCOCH═CH₂and —(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂ wherein n independentlyrepresents a number between 1 and 12; said matrix, when being a polymerof said rhodamine chromophore, hydroxyethyl methacrylate andmethylmethacrylate, comprising a proportion of hydroxyethyl methacrylateto methylmethacrylate of at least 1:1; X is an anion; the matrix being asolid in the shape of a cylinder portion having an axial flat lateralsurface obtained by cutting a cylinder obtained in a cylindrical mold bythe axis thereof; placing the solid in a standard laser cavity,irradiating the matrix for emitting laser radiation, and shifting thesolid, by means of a shifting device, from a first edge of the flatsurface, in pitches of 0.1 to 0.4 mm, to a second edge of the flatsurface, at a rate such that each region of the flat surface isirradiated with a pumping radiation only once, whereby when the secondedge of the flat surface has been reached, shifting is reversed untilsaid first edge is reached, whereby shifting and reversed shifting arerepeated successively, thereby generating laser radiation in a spectralzone selected from ultraviolet, visible or infrared adjacent spectralzones.
 24. The method of claim 23 wherein said unsaturated group isbonded to the carboxyl group in position 2′ by at least one spacerselected from the group consisting of —(OCH₂)_(n) ⁻, (OCH₂CH₂)_(n) ⁻;and —O—(CH₂)_(n) ⁻; wherein n independently represents a number between1 and
 12. 25. The method of claim 23 wherein said rhodamine chromophorehas been synthesized by reacting rhodamine having a free carboxylic acidgroup in position 2′ and an unsaturated halogen derivative selected fromthe group consisting of substituted and unsubstituted allyl halides, andsubstituted or unsubstituted benzyl, comprising an unsaturated group, atleast one of the allyl group and the unsaturated group being capable ofpolymerizing or copolymerizing with at least another monomer.
 26. Themethod of claim 23 wherein the matrix has been prepared by a reaction ofpolymerization or copolymerization with at least another monomer,whereby a solid with the shape of the mold in which the reaction takesplace is formed.
 27. The method of claim 23 where the matrix is used asan active medium for generating laser radiation in a spectral zoneselected from ultraviolet, visible or infrared adjacent spectral zones.28. The method of claim 23 wherein said anion is at least one of OH⁻,Cl⁻, or ClO₄ ⁻.
 29. The method of claim 23 wherein said R is—(CH₂)n-(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂ and n=2.
 30. A method ofgenerating laser radiation using a solid polymeric matrix as an activemedium, the matrix comprising polymerized monomers of a rhodaminechromophore, the monomers having the general formula,

wherein R¹, R², R³, R⁴, R⁵, R⁶ independently are hydrogen or saturatedalkyl groups of 1 to 6 carbons, and wherein R is an unsaturated groupcapable of polymerization or copolymerization, selected from at leastone of the group consisting of —(CH₂)_(n)(p)C₆H₄—CO₂(CH₂)_(n)OCOCH═CH₂and —(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂ wherein n represents anumber between 1 and 12; said matrix, when being a polymer of saidrhodamine chromophore, hydroxyethyl methacrylate and methylmethacrylate,comprising a proportion of hydroxyethyl methacrylate tomethylmethacrylate of at least 1:1; X is an anion; the matrix being asolid is in the shape of a cylinder, the method comprising placing thesolid in a standard laser cavity, irradiating the matrix for emittinglaser radiation, and continuously rotating the solid in pitches of 0.1to 0.4 mm, such that each region of the matrix is irradiated with apumping radiation only once in one total rotation of the solid, therebygenerating laser radiation in a spectral zone selected from ultraviolet,visible or infrared adjacent spectral zones.
 31. The method of claim 30wherein said unsaturated group is bonded to the carboxyl group inposition 2′ by at least one spacer selected from group consisting of—(OCH₂)_(n) ⁻, (OCH₂CH₂)_(n) ⁻; and —O—(CH₂)_(n) ⁻; wherein n representsa number between 1 and
 12. 32. The method of claim 30 wherein saidrhodamine chromophore has been synthesized by reacting rhodamine havinga free carboxylic acid group in position 2′ and an unsaturated halogenderivative selected from the group consisting of substituted andunsubstituted allyl halides, and substituted or unsubstituted benzyl,comprising an unsaturated group, at least one of the allyl group and theunsaturated group being capable of polymerizing or copolymerizing withat least another monomer.
 33. The method of claim 30 wherein the matrixhas been prepared by a reaction of polymerization or copolymerizationwith at least another monomer, whereby a solid with the shape of themold in which the reaction takes place is formed.
 34. The method ofclaim 30 where the matrix is used as active medium for generating laserradiation in a spectral zone selected from ultraviolet, visible orinfrared adjacent spectral zones.
 35. The method of claim 30 whereinsaid anion is at least one of OH⁻, Cl⁻, or ClO₄ ⁻.
 36. The method ofclaim 30 wherein R is —(CH₂)_(n)—(p)C₆H₄—CO₂(CH₂)_(n)OCOC(CH₃)═CH₂ andn=2.
 37. A method according to claim 30, wherein the solid in the shapeof a cylinder which is fastened by center portions of bases such thatwhen the matrix is rotated, the pumped region which is to emit laserradiation, always remains aligned within the laser cavity.